TanDEM-X (TerraSAR-X add-on for digital elevation measurements) is an innovative spaceborne radar interferometer that is based on two TerraSAR-X radar satellites flying in close formation. The primary objective of the TanDEM-X mission is the generation of a consistent global digital elevation model (DEM) with an unprecedented accuracy, which is equaling or surpassing the HRTI-3 specification. Beyond that, TanDEM-X provides a highly reconfigurable platform for the demonstration of new radar imaging techniques and applications. This paper gives a detailed overview of the TanDEM-X mission concept which is based on the systematic combination of several innovative technologies. The key elements are the bistatic data acquisition employing an innovative phase synchronization link, a novel satellite formation flying concept allowing for the collection of bistatic data with short along-track baselines, as well as the use of new interferometric modes for system verification and DEM calibration. The interferometric performance is analyzed in detail, taking into account the peculiarities of the bistatic operation. Based on this analysis, an optimized DEM data acquisition plan is derived which employs the combination of multiple data takes with different baselines. Finally, a collection of instructive examples illustrates the capabilities of TanDEM-X for the development and demonstration of new remote sensing applications.

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TanDEM-X: A Satellite Formation for High-Resolution SAR Interferometry

http://ieeexplore.ieee.org/iel5/4768668/4784008/04784017.pdf

TanDEM-X: A satellite formation for high-resolution SAR interferometry

This paper reviews advanced radar architectures that employ multiple transmit and multiple receive antennas to improve the performance of future synthetic aperture radar (SAR) systems. These advanced architectures have been dubbed multiple-input multiple-output SAR (MIMO-SAR) in analogy to MIMO communication systems. Considerable confusion arose, however, with regard to the selection of suitable waveforms for the simultaneous transmission via multiple channels. It is shown that the mere use of orthogonal waveforms is insufficient for the desired performance improvement in view of most SAR applications. As a solution to this fundamental MIMO-SAR challenge, a new class of short-term shift-orthogonal waveforms is introduced. The short-term shift orthogonality avoids mutual interferences from the radar echoes of closely spaced scatterers, while interferences from more distant scatterers are suppressed by digital beamforming on receive in elevation. Further insights can be gained by considering the data acquisition of a side-looking imaging radar in a 3-D information cube. It becomes evident that the suggested waveforms fill different subspaces that can be individually accessed by a multichannel receiver. For completeness, the new class of short-term shift-orthogonal waveforms is also compared to a recently proposed pair of orthogonal frequency-division multiplexing waveforms. It is shown that both sets of waveforms require essentially the same principle of range time to elevation angle conversion via a multichannel receiver in order to be applicable for MIMO-SAR imaging without interference.

/pdf/mimo-sar-opportunities-and-pitfalls-loj515nyte.pdf

MIMO-SAR: Opportunities and Pitfalls

The focus of this paper is on surveying UAV-based systems for traffic monitoring and management. Although there has been voluminous research on the subject, unmanned aerial vehicles (UAVs) are proven to be a viable and less time-consuming alternative to real-time traffic monitoring and management, providing the eye-in-the-sky solution to the problem.

A survey of unmanned aerial vehicles (UAVs) for traffic monitoring

We introduce the concept and practical design of broadband, ultrathin cloaks based on non-Foster, negatively capacitive metasurfaces. By using properly tailored, active frequency-selective screens conformal to an object, within the realm of a practical realization, we show that it is possible to drastically reduce the scattering over a wide frequency range in the microwave regime, orders of magnitude broader than any available passive cloaking technology. The proposed active cloak may impact not only invisibility and camouflaging, but also practical antenna and sensing applications.

/pdf/broadening-the-cloaking-bandwidth-with-non-foster-42drnlwnqq.pdf

Broadening the cloaking bandwidth with non-Foster metasurfaces.

In this article, we propose an ultrathin and ultrawideband metamaterial (MTM) absorber based on periodically arranged metallic square spirals. The design, characterization, and measurement of the proposal are presented as its equivalent circuit. The lumped elements of the equivalent circuit are extracted using a proposed algorithm based on the least-square method, which presents a straightforward and promising approach and shows a good matching with the electromagnetic simulation. The unit cell of the proposed structure has the square spiral mounted on an FR-4 substrate in front of a conductive plate. The simulated results show an absorptivity of more than 90% from 11.4 to 20.0 GHz, covering the $Ku$ -band for transverse magnetic (TM) and transverse electric (TE) polarizations, and this broadband feature is confirmed by the experimental measurement. Furthermore, the proposed MTM absorber is $\lambda /16.4$ in thickness at the lowest frequency of absorption. The proposed MTM has proper response under oblique incidence from 0° to 50° and shows great performance with regard to the absorbers previously presented in the literature.

An Ultrathin and Ultrawideband Metamaterial Absorber and an Equivalent-Circuit Parameter Retrieval Method

The cloaking efficiency of a finite-size cylindrical transmission-line cloak operating in the X-band is verified with bistatic free space measurements. The cloak is designed and optimized with numerical full-wave simulations. The reduction of the total scattering width of a metal object, enabled by the cloak, is clearly observed from the bistatic free space measurements. The numerical and experimental results are compared resulting in good agreement with each other.

Experimental Characterization of a Broadband Transmission-Line Cloak in Free Space

To ensure mobility, future road traffic management urgently needs actual and reliable information about the road traffic over wide areas in order to keep the traffic moving and the travel time short. Nowadays, outside of motorways the actual traffic situation is almost unknown due to the lack of sensor installations. This is the background for the TRAMRAD (Traffic Monitoring with Radar) project. TRAMRAD aims at profiting from research and development in earth observation and advances in radar remote sensing techniques to define realizable future air- or spaceborne sensor systems for the wide area monitoring of road traffic. The project comprises the necessary theoretical and practical investigations, as well as experimental campaigns with airborne instruments. The paper describes the requirements for the systems and the concepts being investigated. In particular, it discusses the complex detection conditions, the requirements on the radar instrument and the methods for processing the data. Possible system concepts are described and their capabilities are discussed.

Air- and spaceborne monitoring of road traffic using SAR moving target indication - Project TRAMRAD

To meet the challenges of ever increasing road traffic and the associated economic and sociological impacts, new techniques and technologies for better traffic management are needed. The TRAMRAD project (Traffic Monitoring with space-based Radar) aims to profit from research and development in earth observation and advances in radar remote sensing techniques to define a future space-based sensor system for the wide-area monitoring of road traffic. The paper describes the requirements for the system and the concepts being investigated. In particular, it discusses the complex detection conditions, the requirements on the radar instrument and the methods for processing the data. Possible system concepts are described and their capabilities are discussed.

An autonomous, non-cooperative, wide-area traffic monitoring system using space-based radar (TRAMRAD)

The knowledge of electrical material parameters for microwave frequencies is of great importance for several applications, e.g. microwave remote sensing and wave propagation. Therefore high precision transmission and reflection measurements on material samples are necessary. In the case of layered media the determination of effective material parameters is aspired. The existing free space measurement facilities of the Institute are presented. Experimental results on flat samples are shown.

Erich Kemptner

Papers

An Ultrathin and Ultrawideband Metamaterial Absorber and an Equivalent-Circuit Parameter Retrieval Method

Experimental Characterization of a Broadband Transmission-Line Cloak in Free Space

Air- and spaceborne monitoring of road traffic using SAR moving target indication - Project TRAMRAD

An autonomous, non-cooperative, wide-area traffic monitoring system using space-based radar (TRAMRAD)

Free space material characterization for microwave frequencies